Bone conduction receiver



s. F. LYBARGER 2,230,500 BONE CQNDUCTION RECEIVER Filed Jan. 14, 1939.20 Jg' l Patented Feb. 4, i941 UNiTao STATES 2,230,500 some comiuo'rronBE Lybarger Application January 14, 1939, Serial No. 251,39

7 Claims. (01. 179 -107) This invention relates to hearing-aid receiversfor hard-of-hearing people, and more particularly to bone conductionreceivers of the direct action type.

A commercial form of thistype of receiver is illustrated in my patentapplication Serial No. 233,343, filed October 5, 1938. As there shown,electromagnetic means, including a pole-piece, is mounted in a casewhich has an open side. Extending across this open side of the case is arigid plate-like vibratory member that is resiliently supported adjacentthe pole-piece with an air gap between them. The case is supported by ahead-band for holding the vibratory member against a hearing-inducingbone of the user. To

- permit the vibratory member to vibrate relative to the case, it isspaced from the case, and this space is closed by a gasket.

In this type of receiver where the area of the vibratory surfaceengaging the head is approximately the same size as the rest of thereceiver, the problem of air radiation from the surfaces of the receiverbecomes of considerable importance. That is, with a gasket which offersconsiderable resistance to passage of air through it, the, receiver isin effect a closed cavity the surfaces of which vibrate. It is thereforesimilar to a telephone receiver and, like the latter, has a fairly highradiation eiliciency, especially at high frequencies. Such a receiveroperates satisfactorily as a bone conduction receiver as long as thereis not suiiicient amplification in the system to cause the soundradiated by the receiver into the air to be transmitted through the airback to the microphone where it is re-amplifled and presented again tothe receiver. With such a condition howling or acoustic feed-back wouldbe .produced. In cases where themicrophone is located at a considerabledistance from the receiver, as in a theater or church where a wiringdistribution system is used from a microphone on the platform, thiseflect would not impair the bone conduction reception, although it mightproduce enough radiated sound to disturb the people in the immediatevicinity of the receiver. But in general the microphone is worn on theupper part of the body of the user where it is relatively close to thereceiver, and can therefore more or less easily pick up sound radiationstherefrom, if they are loud.

It is among theobjects of this invention to provide a bone conductionreceiver which can be used with very high amplification withoutproducing acoustic feed-back to the microphone, and in which the efiectof sound radiation from surfaces of the receiver is minimized. Otherobjects are to provide such a' receiver with means that permits freedomof air iiow in and out of the case but prevents dust and other foreignmatter from fouling the air gap.

In accordance with this invention, a substantially rigid vibratorymember adapted to be pressed against a hearing-inducing bone of ahard-of-hearing person, such as the mastoid bone, is disposed across anopening in a case that contains an electromagnet. The vibratory memberis so supported by resilient means mounted in the case that an air gapis formed between the electromagnet and the vibratory member. Thevibratory member is spaced a suiiicient distance from the case to permitenough freedom of ,air flow in and out of the case to avoidobjectionable sound radiation therefrom. That is, the area of thereceiver which is effective in radiating sound is materially reducedbecause air is more or less freely admitted to both sides of thevibratory member, whereby the sound radiated from one side of thevibratory member tends to cancel the sound of opposite phase radiatedfrom its otherside. In one form of the invention the walls of the spacebetween the case and vibratory member are provided with stepped orotherwise irregularly shaped portions to prevent foreign objects frombeing inserted through that space. A more desirable form of theinvention seals this space with a flexible or resilient gasket thatprevents obiectionable foreign particles, such as dust, from enteringthe case, but which is porous enough to offer only a small amount ofresistance to flow of air in and out of they case. In the preferredembodiment of the invention the space between the vibratory member andcase is unobstructed by any gasket, but a sealing member surrounds theair gap itself in close proximity thereto so as to prevent foreignmatter from fouling it. This gasket encloses a'very small volume of airand therefore forms only a small closed cavity behind the vibratorymember, whereby the eifective radiation area of the receiver is greatlyreduced.

The invention is illustrated in the accompanying drawing in which Fig. 1is a view illustrating the positions in which a bone conduction receiverand a microphone are generally worn by a hardof-hearing person; Fig. 2is an enlarged plan view of the receiver as seen when it is lying withits vibratory member face down; Figs. 3 and 4 are longitudinal andtransverse sections, respectively, taken on the lines III-III and IV-IVof Fig. 2; Fig. 5 is an enlarged perspective view integral case I, whichis approximately rectangula in cross section, has top and depending side4 and end walls and an open bottom. Mounted in this-case iselectromagnetic means for driving a vibratory member in accordance withvariations in electric current caused by a microphone 2 (Fig. 1)responding to sound waves. The electromagnetic means or system includesa permanent bar magnet I to one endoi' which is secured a metalpole-piece 4 that has a portion extending substantially at right anglesto the magnet and towards the open bottom of the case. The inner end ofthe pole-piece is preferably disposed be- 1 tween the magnet, to whichit is connected by screws 5, and the top of the case. The pole-piece andmagnet are rigidly attached to the top of the case by screws 6 threadedinto the pole-piece. and

by screws 1 connected to a spacer member I between the opposite end ofthe case and the magnet to which the spacer member is attached by screws9. The outwardly projecting portion of the pole-piece is encircled by anelectromagnetic coil ll connected by wires l2 to metal spring strips I3secured at one end to the sides 'of the case with their other endsprojecting part way across a pair of openings ll through the adjoiningend wall of the case. These openings are adapted to receive electricplugs I 6 that engage springs l3 and connect them with the microphone 2or amplifier unit (not shown) of the hearing-aid system.

Extending across the open bottom of the case and forming a covertherefor is a rigid platelike button or vibratory member I! adapted toen a e a hearing-inducing bone, such as the mastoid bone, of ahard-oi-hearing' person. Of course. engagement with a bone means contactwith the skin overlying the bone. This vibratory member is supportedfrom the interior of the case in predetermined spaced relation with theouter end of thepole-piece by means of spring It which is resilientwholly or in part to permit the vibratory member to be vibrated by theelectromagnet. As the vibratory member is r gid, it must also be spaceda slight distance from case I so that its movements will not beprevented by the case. Being a direct action ty e receiver, thevibratory member is pressed a ainst the head or other bone structure bythe case through sprin IS, the case being directly su orted by suitablemeans, such as a headband. To prevent spring l8 from being sprung out ofshape in case someone pinches the vibrating member and case together atthe end o posite to the pole-piece. the inner face of the vibratorymember is provided with a projection I! that is spaced only a slightdistance from the end wall of the case.

As shown in Figs- 1 and 2, the band includes a curved strip 2. of springmetal adapted to M over the head, and a yoke 2| pivotally connected tothe metal strip and straddling the case. The ends of the yoke areprovided with pins 22 that are pivotally mounted in holes 23 in theopposite sides of the case so that the case can tilt vertically relativeto the yoke to better adjust itself to the contour of the head. Theouter surface of the vibratory member is preferably curvedlongitudinally to give a greater area of contact with the head in orderto rest more comfortably against it. and also to better retain thevibratory member in position.

Spring is is connected to the vibratory member adjacent the pole-pieceby screws 21, and extends away from both of them towards the g oppositeend of the case to which it is connected either directly or indirectly.Preferably this inner end of the spring is connected to magnet bar 3 atthe end opposite to the pole-piece by screws 9. By making spring is ofmagnetic metal its outer end can serve as an armature for theelectromagnetic system when extended across the end of the pole-piece,as shown in Pig. 3. In

- spite of the pole-piece being rigidly mounted in the case, it can besprung away from magnet '3 iii a very slight amount by set screw 28 toincrease the width of air gap 2'.

It is a feature of this invention that the vibratory member is spacedfar-enough from case I to permit suiilcient freedom of air flow into andout of the case for diminishing radiation of sound through the air fromthe surfaces of the receiver to a point where the radiations are notobjectionable to the user or those near him. The vibratory member orcase therefore corresponds to a vibratory plate freely suspended in airso that sound radiated from one side of the plate tends to cancel thatradiated from the other side and which is of opposite phase. As shown inFigs. 3 and 4, the walls of the space between the vibratory member andcase are preferably provided with stepped portions 3| forming a seriesof right angles so that foreign objects can not readily be insertedthrough this space into the receiver.

It is also highly desirable to protect air gap 2 against being fouled bydust or other foreign matter that may find its way into the receiverthrough the small space between vibratory member and case. In accordancewith this invention 40 this protection is obtained by surrounding theair gap itself with a sealing member 32. This member is flexible orresilient so that it will not interfere with the necessary vibrations ofthe vibratory member, and it engages the electric coil 8 and spring llbelow it in order to seal the space 2 immediately surrounding the airgap. The annular sealing member is very small so that it will encloseonly a small volume of air, whereby only a very small area of thevibratory member forms a wall of a sealed cavity or chamber.Consequently, the eflective air radiation surface of the relativelylarge plate-like vibratory member or of the case is reduced to such anextent that the sound radiated by it through the air is too weak tocause acoustic feed-back or to disturb people near the hard-of-hearingperson.

Preferably, the sealing member is substantially of the shape shown inFig. 5. That is, it has spaced upper and lower marginal portions 33extending laterally outwardly in the same general direction from thecentral portion of the seal. This shape makes the seal very flexible forits size, and the marginal portions tend to spread apart and engagespring I! and the ad- .Iacent end face of the coil between which theseal is most effectively located. It is also desirable to cement themarginal portions of the seal to the surfaces they engage.

A receiver made in accordance with this invention has the advantage ofthe comfort, of a relatively large plate-like surface engaging the head,without the disadvantage of acoustic feedback or excessive soundradiation through air generally found with receivers of this type. The75 like through the space between case and vibratory member, and thevital air gap is prevented from being fouled by small foreign particles,such as dust.

In the modification shown in Fig. 6, sealing member 32 and steppedportions 3| of the receiver may be dispensed with, and the function ofboth performed bya resilient or flexible gasket 36 mounted in the spacebetween case wall and vibratory member. To permit flow of air into andout of the case to be free enough to accomplish the object of thisinvention, this gasket must be formed of a material of relatively greatporosity. However, the 'gasket must not be so porous as to permitpenetration by dust particles and the like which might foul the air gap.A. material that has been found suitable for this gasket is a porousfelt, although there are doubtless other materials, such as muslin,etc., that would be satisfactory.

According to the provisions of the patent statutes, I have explained theprinciple and construction of my invention and have illustrated anddescribed what I now consider to represent its best embodiments.However, I desire to have it understood that, within the scope of theappended claims, the invention may be practiced otherwise than asspecifically illustrated and described. v

I claim:

1. A bone conduction receiver comprising a case open at one side, arelatively large plate-like vibratory member forming a closure for saidopening and overlapping the case but spaced from the case sufficientlyto permit unrestricted I flow of air into and out of the case to renderair radiation of sound from the receiver unobjec- Iii) tionable whensaid vibratory member is positioned against the head, the space betweensaid case and vibratory member being entirely open,

electrically controlled means mounted in the.

' case for actuating said vibratory member, and

resilient means in the case supporting the vibratory member.

2. A bone conduction receiver comprising a case having an open side,electromagnetic means a unobjectionable, and resilient means in the casesupporting the vibratory member, the walls of the space between the caseand vibratory member being formed with stepped portions'for preventingthe insertion of foreign objects through said space. a

3. A bone conduction receiver comprising a case having an opening in oneside, a pole-piece mounted in the case, a vibratory member extendingacross said opening and spaced from the case, resilient means in thecase supporting the vibratory member adjacent the pole-piece with an airgap between them, and a flexible sealing member surrounding said air gapin close proximity thereto.

4. A bone conduction receiver comprising a case having an opening in oneside, a pole-piece mountedin the case, an electric coil surrounding thepole-piece, a vibratory member forming a closure for said opening andspaced from the case, resilient means in the case supporting thevibratory member adjacent the pole-piece with an air gap between them,and a flexible sealing member surrounding said air gap in closeproximity thereto, said member having laterally extending spacedmarginal portions connected to the vibratory member and the adjacent endof the coil.

5. A bone conduction receiver .comprising a case having an opening inone side, a pole-piece mounted in the case, an electric coil surroundingthe pole-piece, a vibratory member forming a closure for said openingand spaced from the case, the walls of the space between the case andvibratory member being formed with stepped portions for preventing theinsertion of foreign objects throughsaid space, resilient means in thecase supporting the vibratory member adjacent the pole-piece with an airgap between them, and a flexible sealing member surrounding said air gapin close proximity thereto, said member having laterally extendingspaced marginal portions connected, to the vibratory member and theadjacent end of the coil.

'6. A bone conduction receiver comprising a case having an opening inone side, a pole-piece mounted in the case, a vibratory member extendingacross said opening and spaced from the case, resilient means in thecase supporting the vibratory member adjacent the pole-piece with an airgap between them, and means entirely inside the case protecting the airgap from foreign matter.

7. A bone conduction receiver comprising a case having an opening in oneside, a pole-piece mounted in the case, an electric coil surrounding thepole-piece, a vibratory member forming a closure for said opening andspaced from the case, resilient means in the case supporting thevibratory member adjacentthe pole-piece with an air gap between them,and a flexible sealing member surrounding said air gap in closeproximity thereto between the end face of the coil and the vibratorymember.

SAMUEL F. LYBARGER.

